Liquid crystal display and method of manufacturing the same

ABSTRACT

A liquid crystal display includes a first substrate, a second substrate, and a liquid crystal layer. The first substrate includes a first insulating substrate, in which a pixel area is defined, a gate line formed on the first insulating substrate, a data line crossing the gate line, and a thin film transistor connected to the gate line and the data line. The second substrate is opposite to the first substrate. The liquid crystal layer is interposed between the first and second substrates and includes a liquid crystal composition with a nematic-isotropic phase transition temperature (Tni) of 79° C. or above.

CROSS-REFERENCE TO RELATED APPLICATION

This application relies for priority upon Korean Patent Application No.2009-84034 filed on Sep. 7, 2009, the contents of which are hereinincorporated by reference in their entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a liquid crystal display and a methodof manufacturing the same.

2. Description of the Related Art

A liquid crystal display includes a liquid crystal layer interposedbetween two substrates. The liquid crystal display is provided withelectrodes which are formed on the substrates. The liquid crystal layerincludes liquid crystal molecules. The alignment of the liquid crystalmolecules is changed according to the electric field generated by theelectrodes. Changing the alignment of the liquid crystal moleculesadjusts the quantity of light passing through the liquid crystaldisplay. Accordingly, an image is displayed.

Display apparatuses employing liquid crystal displays have beenextensively used in devices such as mobile phones, personal digitalassistants, personal computers, and televisions. The liquid crystaldisplays are often specifically developed to be suitable for use in theparticular devices in which they are employed.

Recently, the use of portable device, including portable notebookcomputers has been increasing. Such devices require superior mobileconvenience, and thus there is demand for liquid crystal displays thatsatisfy the requirements of low power consumption and high responsespeed.

SUMMARY

The present invention relates to a liquid crystal display havingimproved display quality.

The present invention also relates to a method of manufacturing theliquid crystal display.

In one aspect, the liquid crystal display includes first and secondsubstrates opposite to each other and a liquid crystal layer interposedbetween the first and second substrates. The first substrate includes afirst insulating substrate comprising a pixel area, a gate line on thefirst insulating substrate, a data line crossing the gate line, and athin film transistor connected to the gate line and the data line. Theliquid crystal layer comprises a liquid crystal composition whichincludes 31 weight % to 48 weight % of a neutral liquid crystalcomprising at least one compound selected from the group of compoundsrepresented by formula 1 below, 8.5 weight % to 18 weight % of firstpolar liquid crystal comprising at least one compound selected from thegroup of compounds represented by formula 2 below, and 42 weight % to 51weight % of second polar liquid crystal comprising at least one compoundselected from the group of compounds represented by formula 3 below.

In the case of the compounds of formula 1, formula 2 and formula 3, X isan alkyl, alkoxy, or alkenyl group having two to five carbon atoms, andY is an alkyl or alkenyl group having two to five carbon atoms.

The liquid crystal composition has a nematic-isotropic phase transitiontemperature (Tni) of 79° C. or above. The liquid crystal compositionincludes a cholesteric liquid crystal composition. The cholestericliquid crystal composition includes a chiral liquid crystal having apitch of about 50 μm to about 70 μm. The liquid crystal composition haspositive dielectric anisotropy in a range of about 8 to about 15. Adriving voltage of about 3.0 V to about 3.6 V may be applied to theliquid crystal layer.

The data line formed on the first substrate has a thickness of 1500 Å orless. The data line may include aluminum (Al).

A protective layer is formed on the first insulating substrate, the gateline, the data line, and the thin film transistor. The protective layermay have a raised portion with a height of about 1400 Å or less on anarea where the data line is disposed. The raised portion has a flat topsurface and inclined lateral sides, and an angle between at least one ofthe lateral sides and a straight line perpendicular to the flat topsurface is in a range of about 50° to about 70°.

In another aspect, a pixel electrode is provided in the pixel area ofthe first substrate. The pixel electrode is connected with a drainelectrode of the thin film transistor. A storage line spaced apart fromthe gate line is provided on the first insulating substrate. A storageelectrode branches from the storage line to partially overlap with thepixel electrode and the data line. A gate insulating layer is interposedbetween the data line and the storage electrode.

In still another aspect, a pixel electrode is provided in the pixel areaof the first substrate. The pixel electrode is connected with a drainelectrode of the thin film transistor. First and second floating storageelectrodes are provided on the first insulating substrate. First andsecond floating storage electrodes are spaced apart from the gate line.The first and second floating storage electrodes partially overlap withthe pixel electrode, respectively, and are spaced apart from each otherwith the data line interposed between the floating electrodes whenviewed in a plan view. A gate insulating layer is formed on the gateline, and the first and second floating storage electrodes are formed onthe gate insulating layer.

The liquid crystal display is manufactured by forming first and secondsubstrate, and inserting a liquid crystal layer including a liquidcrystal composition between the two substrates.

A gate line, a data line crossing the gate line to define a pixel area,and a thin film transistor connected to the gate line and the data lineare formed on a first insulating substrate. Then, a first alignmentlayer is formed on the first insulating substrate having the thin filmtransistor, and the first alignment layer is rubbed to form the firstsubstrate. The second substrate is formed by forming a second alignmentlayer on a second insulating substrate and rubbing the second alignmentlayer.

The data line has a height of 1500 Å or less.

A protective layer, which has a raised portion with a height of 1400 Åor less over the data line, is formed on the first insulating substrate.The raised portion on the data line has a flat top surface and inclinedlateral sides, and an angle between at least one of the lateral sidesand a straight line perpendicular to the flat top surface is in a rangeof about 50° to about 70°.

The first and second alignment layers are rubbed with a rubbing rollrotated at a rate of about 1500 rpm to about 2000 rpm, and a rubbingdepth of the rubbing roll from a surface of the first and secondalignment layers may be in a range of about 0.20 mm to about 0.30 mm.

The rubbing roll is wound with a rubbing cloth. The rubbing clothincludes a ground cloth formed by warps and wefts or a cloth having afiling yarn woven in a direction of the warp of the ground cloth.

The liquid crystal display as disclosed herein has reduced domaindefects, thereby improving display quality. The liquid crystal displayis manufacture through the method disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will becomereadily apparent by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a plan view showing a liquid crystal display according to afirst embodiment;

FIG. 2 is a sectional view taken along line I-I′ of FIG. 1;

FIG. 3 is a plan view showing a liquid crystal display according to asecond embodiment; and

FIG. 4 is a sectional view taken along line II-II′ of FIG. 3.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a liquid crystal display and method of manufacturing thesame according to exemplary embodiments will be described with referenceto accompanying drawings.

However, the present invention is not limited to the followingembodiments but includes various applications and modifications.Therefore, the scope of the present invention should not be limited tothe following embodiments. In addition, the size of the layers andregions of the attached drawings along with the following embodimentsare simplified or exaggerated for precise explanation or emphasis, andthe same reference numeral represents the same component.

FIG. 1 is a plan view showing a liquid crystal display according to afirst embodiment, and FIG. 2 is a sectional view taken along line I-I′of FIG. 1.

Referring to FIGS. 1 and 2, the liquid crystal display includes a firstsubstrate 100, a second substrate 200 opposite to the first substrate100, and a liquid crystal layer 300 interposed between the first andsecond substrates 100 and 200, respectively.

The first substrate 100 includes a first insulating substrate 110 whichhas a plurality of pixel areas PAs. Gate lines GLs and data lines DLsthat cross the gate lines GLs are disposed on the first insulatingsubstrate 110 to define pixel areas PAs. For the purpose of explanation,FIGS. 1 and 2 show a single pixel area having one gate line GL and onedata line DL together with a portion of an adjacent pixel area. Becauseall of the pixel areas PAs in the liquid crystal display havesubstantially the same structure, only the one pixel area shown in FIGS.1 and 2 will be described below, for convenience of explanation.

Referring to FIG. 1, the first insulating substrate 110 is providedthereon with the gate line GL, the data line DL, a thin film transistorTR, a pixel electrode PE, a storage line STL, and a storage electrodeSTE.

The gate line GL extends in a first direction D1, and the data line DLextends in a second direction D2 perpendicular to the first directionD1.

The thin film transistor TR includes a gate electrode GE branching fromthe gate line GL, an active pattern 150 formed over the gate electrodeGE, a source electrode SE branching from the data line DL to overlapwith the active pattern 150, and a drain electrode DE spaced apart fromthe source electrode SE. The drain electrode DE overlaps with the activepattern 150.

The pixel area PA is provided with the pixel electrode PE. The pixelelectrode PE is connected to the drain electrode DE.

The storage line STL extends substantially in the first direction D1. Inaddition, the storage line STL is spaced apart from the gate line GL andis adjacent to the gate line GL.

The storage electrode STE branches from the storage line SL to extend inthe second direction D2. The storage electrode STE overlaps with aportion of the pixel electrode PE and the data line DL. In more detail,the storage electrode STE overlaps with a portion of each of pixelelectrodes PE adjacent to and spaced apart from each other, and overlapswith the data line DL, which is between the two adjacent pixelelectrodes PE. The portion of the pixel electrodes PE that the storageelectrode STE overlaps is typically along the length of an edge sectionof the pixel electrode PE in the D2 direction. Accordingly, the storageelectrode STE forms a storage capacitor together with each pixelelectrode PE.

The storage electrode STE blocks light that travels from underneath thefirst insulating substrate 110 toward the liquid crystal layer, so thatsuch light does not pass through the liquid crystal layer that is overthe storage electrode STE and data line DL. Therefore, the size of thearea of a black matrix that is formed on the second substrate 200 inorder to block light can be reduced. Thus the aperture ratio of theliquid crystal display is improved.

Referring to FIG. 2, the storage electrode STE is provided on the firstinsulating substrate 110, and a gate insulating layer 120 is provided onthe storage electrode STE. The data line DL is provided on the gateinsulating layer 120. The data line DL overlaps with the storageelectrode STE.

A protective layer 130 is disposed on the data line DL. The pixelelectrodes PE are formed on the protective layer 130 such that portionsof the pixel electrodes PE adjacent to each other overlap with thestorage electrode STE.

A first alignment layer 140 is provided on the protective layer 130 andthe pixel electrode PE, which is formed on the protective layer 130. Thefirst alignment layer 140 adjusts the pre-tilt angle of liquid crystalmolecules existing in the liquid crystal layer 300.

As shown in FIG. 2, the data line DL has a predetermined thickness t1.The term “thickness” refers to a height (distance) from a top surface ofa layer on which an element is formed to a top surface of the elementitself. According to the first embodiment of the present invention, thethickness t1 of the data line DL may be 1500 Å or less. The data line DLis made of a conductive material. The data line DL may include a metalor a metal alloy and include a single layer or a multi-layer. The metalmay include aluminum (Al) or chromium (Cr).

The protective layer 130 has a raised portion RP that protrudes by apredetermined thickness H1 as a result of the thickness t1 of the dataline DL.

The raised portion RP of the protective layer 130 on the data line DLmay have the thickness H1 of about 1400 Å or less. In addition, in orderto offset a height of the raised portion RP of the protective layer 130,the storage electrode STE may have a thickness of about 1200 Å or less.

The raised portion RP on the data line DL has a flat top surface andinclined lateral sides, and an angle θ between one of the lateral sidesand a straight line perpendicular to the flat top surface may be about50° to about 70°.

The data line DL and the raised portion RP of the protective layer 130have thicknesses of about 1500 Å or less and about 1400 Å or less,respectively. If the height of the raised portion RP on the data line DLexceeds a predetermined value, for example, if the height is over 4000Å, the alignment layer 140 is not formed uniformly in the raised portionRP. While not wishing to be bound by any theory, it is understood thatan alignment layer interacts with the liquid crystal molecules in theliquid crystal layer at the surface of the alignment layer to align theorientation of the liquid crystal molecules, and create what is referredto as a “pre-tilt angle.” The “pre-tilt angle” is the angle oforientation of the liquid crystal molecules, and is typically the anglebetween the long axis of the liquid crystal molecules and the surface ofthe alignment layer. The pre-tilt angle determines gray scale contrastin liquid crystal displays. After an alignment layer is formed, itundergoes a rubbing process, which is believed to create the surfaceproperties on the alignment layer necessary to properly orient theliquid crystal molecules to the pre-tilt angle. Thereafter, the lateralsides of the raised portion RP may not be aligned when an alignmentlayer rubbing process to form a pre-tilt angle is performed. Since thelateral sides of the raised portion has no or insufficient alignmentforce for the liquid crystal, light leakage may occur.

The description of the embodiment has focused on the raised portion RPon the data line DL. However, the same principles may be applied, forexample, to the gate line GL. A raised portion on the gate line GL mayhave a thickness equal to or less than the thickness of the raisedportion RP on the data line DL. For example, the raised portion on thegate line may have a thickness of about 1200 Å for the same reasonsdescribed above with respect to the raised portion RP on the data lineDL. A black matrix BM is formed on a second insulating substrate 210 toblock light. Red and green color filters R and G are formed on the blackmatrix BM corresponding to the pixel areas PA, respectively. Althoughthe red and green color filters R and G are shown in FIG. 2, a bluecolor filter (not shown) is typically also formed on the secondinsulating substrate 210 in addition to the red and green color filtersR and G.

A common electrode 230 is formed on the red and green color filters Rand G. The common electrode 230 faces the pixel electrode PE, and,together with the pixel electrode PE, forms an electric field.

A second alignment layer 240 is formed on the common electrode 230 tocontrol the pre-tilt angle of the liquid crystal layer 300.

With respect to the liquid crystal layer 300, according to oneembodiment, low power consumption in the liquid crystal display deviceis achieve through the use of a liquid crystal composition having highdielectric anisotropy, such that the liquid crystal display can bedriven at a low driving voltage.

The liquid crystal composition includes at least one liquid crystalcompound selected from the compounds in each group of the followingformulas 1 to 3, respectively. Formula 1 represents a neutral liquidcrystal corresponding to 31 weight % to 48 weight % of the whole liquidcrystal composition. Formula 2 represents a first polar liquid crystalcorresponding to 8.5 weight % to 18 weight % of the whole liquid crystalcomposition. Formula 3 represents a second polar liquid crystalcorresponding 42 weight % to 51 weight % of the whole liquid crystalcomposition. The first polar liquid crystal has a polarity greater thanthat of the second polar liquid crystal.

wherein X is an alkyl, alkoxy, or alkenyl group having 2 to 5 carbonatoms, and Y is an alkyl or alkenyl group having 2 to 5 carbon atoms.

The liquid crystal composition has a nematic-isotropic phase transitiontemperature (Tni) of 79° C. or more. The liquid crystal composition haspositive dielectric anisotropy of about 8 to about 15. A driving voltageof about 3.0 V to about 3.6 V is preferably applied to the pixelelectrode PE in order to drive the liquid crystal layer 300. The on/offresponse speed of the liquid crystal layer may be about 16 ms or less.

According to the one embodiment of the present invention, the liquidcrystal composition may include a cholesteric liquid crystal compositionhaving chiral dopants. In this case, the pitch of the cholesteric liquidcrystal may be about 50 μm to about 70 μm.

The liquid crystal display having the structure described is driven whena common voltage is supplied to the common electrode 230, and a pixelsignal from the data line DL is supplied to the pixel electrode PE inresponse to a scan signal supplied from the gate line GL. As a result,an electric field is formed between the common electrode 230 and thepixel electrode PE, and the liquid crystal is rotated by the electricfield to change the transmittance of light through the liquid crystaldisplay, resulting in an image being displayed.

According to one embodiment, the thickness t1 of the data line DL isreduced such that the height H1 of the raised portion RP is optimizedwith respect to the alignment layer and the liquid crystal composition.Accordingly, the height H1 of the raised portion RP of the protectivelayer 130 is reduced, so that misalignment of the liquid crystal layer300 is reduced. In addition, the lateral sides of the raised portion RPare formed at an inclination angle of about 50° to about 70°, so thatdefects caused by rubbing are reduced.

In addition, according to the present embodiment, since the liquidcrystal composition having a high Tni of 79° C. or more is used,misalignment of the liquid crystal molecules may be reduced at hightemperatures, for example, temperatures over 80° C. However, since theliquid crystal composition having high dielectric anisotropy and highTni has a smaller pre-tilt angle than other liquid crystal compositions,liquid crystal molecules of the composition may not return to theiroriginal positions upon the application, or non-application, of theelectric field. Also according to the present embodiment, even thoughdefects can occur at the raised portion RP, since the thickness of thedata line DL and/or the protective layer 130 on the data line DL isadjusted in the present embodiment, such defects are reduced, and thedriving of the liquid crystal composition is facilitated.

FIG. 3 is a plan view showing a liquid crystal display according to asecond embodiment of the present invention, and FIG. 4 is a sectionalview taken along line II-II′ of FIG. 3. Hereinafter, the liquid crystaldisplay according to the second embodiment will be described whilefocusing on differences between the first and second embodiments inorder to avoid redundancy. The same reference numerals will be used todesignate like elements between the two embodiments.

According to the second embodiment of the present invention, the storageelectrode STE has a structure different from that of the firstembodiment. Also, the height of the raised portion RP of the protectivelayer 130 is smaller than that of the first embodiment.

Referring to FIG. 3, the first insulating substrate 110 is providedthereon with the gate line GL, the data line DL, the thin filmtransistor TR, the pixel electrode PE, the storage electrode STE, afirst floating storage electrode FSTE1, and a second floating storageelectrode FSTE2.

The gate line GL extends in the first direction D1. A portion of thegate line GL protrudes into a portion of the pixel area PA below (i.e.located in the D2 direction with respect to the GL) the gate line andextends in the second direction D2 to overlap with the pixel electrodePE formed in the succeeding pixel area PA, thereby forming the storageelectrode STE. The storage electrode STE forms a storage capacitor witheach pixel electrode PE. The first floating storage electrode FSTE1 andthe second floating storage electrode FSTE2 are disposed over a portionof the pixel electrode PE along an edge section to the pixel electrodePE in the D2 direction with the data line DL interposed between the twofloating storage electrodes FSTE1 and FSTE2. The first floating storageelectrode FSTE1 and the second floating storage electrode FSTE2partially overlap with the pixel electrodes PE, respectively. The firstand second floating storage electrodes FSTE1 and FSTE2 include the samematerial as that of the gate line GL. The first and second floatingstorage electrodes FSTE1 and FSTE2 are formed on the same layer as thegate line GL while being spaced apart from the gate line GL at apredetermined distance.

Referring to FIG. 4, the first and second floating storage electrodesFSTE1 and FSTE2 are formed on the first insulating substrate 110, andthe gate insulating layer 120 is formed on the first and second floatingstorage electrodes FSTE1 and FSTE2. The data line DL is formed on thegate insulating layer 120 such that the data line DL does not overlapwith the first and second floating storage electrodes FSTE1 and FSTE2.

The protective layer 130 is formed on the data line DL, and the pixelelectrodes PE are formed on the protective layer 130. The first floatingstorage electrode FSTE1 overlaps with a portion of one of the adjacentpixel electrodes PE, and the second floating storage electrode FSTE2overlaps with a portion of the other of the adjacent pixel electrodesPE. The pixel electrodes PE overlap with the first and second floatingstorage electrodes FSTE1 and FSTE2 to form capacitors, respectively. Thecapacitors are storage capacitors supplementing charges discharged fromthe liquid crystal capacitors that are formed by the pixel electrodes PEand the common electrode 230. Since the first and second floatingstorage electrodes FSTE1 and FSTE2 are spaced apart from the data lineDL when viewed in a plan view, capacitances that are the result ofparasitic capacitors formed between the first and second floatingstorage electrodes FSTE1 and FSTE2 and the data line DL are reduced. Inaddition, the first and second floating storage electrodes FSTE1 andFSTE2 block light transmitted upwardly through the display device, andthus reduce light leakage. Such light leakage is caused by a fringefield at an end portion of the pixel electrode PE due to potentialdifference between an area where an electric field is applied and anarea wherein an electric field is not applied.

The raised portion RP of the protective layer 130 on the data line DLhas a thickness H2 that varies according to a thickness t2 of the dataline DL. An upper portion of the protective layer 130 on the data lineDL protrudes to form the raised portion RP.

According to the second embodiment of the present invention, the dataline DL may have a thickness of about 1500 Å or less, and the raisedportion RP of the protective layer 130 may have a thickness of about1400 Å or less. In order to minimize the thickness of the raised portionRP of the protective layer 130, the first and second floating storageelectrodes FSTE1 and FSTE2 are formed at a thickness of about 1200 Å orless. The raised portion RP on the data line DL has a flat top surfaceand inclined lateral sides, and an angle θ between one of the lateralsides and a straight line perpendicular to the flat top surface may beabout 50° to about 70°.

According to the second embodiment of the present invention, since thefirst and second floating storage electrodes FSTE1 and FSTE2 do notoverlap with the data line DL, respectively, a height of the raisedportion RP of the protective layer 130 is reduced as compared with thatof the first embodiment. Accordingly, misalignment of liquid crystalmolecules at the raised portion RP is also reduced.

The liquid crystal displays having the structure described herein aremanufactured by forming the first and second substrates and interposingthe liquid crystal layer including the liquid crystal compositionsbetween the two substrates. Hereinafter, a method of manufacturing theliquid crystal display according to the first embodiment of the presentinvention will be described with reference to FIGS. 1 and 2. Although amethod of manufacturing the liquid crystal display according to thesecond embodiment is not described in detail herein, one of skill in theart will understand that the liquid crystal display according to thesecond embodiment may be manufactured by the same process as describedfor the first embodiment, with the exception that, when forming thefloating storage electrodes FTSE1 and FTSE2, a pattern having adifferent shape from that used in the first embodiment for forming thestorage electrode STE is employed.

The first insulating substrate 110 is provided thereon with the gateline GL, the gate electrode GE, the storage line STL, and the storageelectrode STE. The gate insulating layer 120 is formed on the firstinsulating substrate 110 having the gate line GL, the storage line STL,and the storage electrode STE. The gate line GL, the gate electrode GE,the storage line STL, and the storage electrode STE may be formed bydepositing a conductive material on the entire surface of the firstinsulating substrate 110 and then patterning the resultant structurethrough a photolithography process. The gate line GL, the storage lineSTL, and the storage electrode STE may have a height of about 1200 Å orless.

Next, after depositing a semiconductor layer including amorphous siliconon the gate insulating layer 120, the resultant structure is selectivelypatterned, thereby forming an active layer 150.

Then, after depositing a conductive layer on the entire surface of thefirst insulating substrate 110, the conducive layer is patterned througha photolithography process, thereby forming the data line DL, the sourceelectrode SE, and the drain electrode DE. The data line DL may have athickness of about 1500 Å or less.

Subsequently, the protective layer 130 is formed on the first insulatingsubstrate 110 and a contact hole is formed to expose a portion of theprotective layer 130. The protective layer 130 is formed on the dataline DL such that the raised portion RP has a height of about 1400 Å orless. The raised portion RP on the data line DL has a flat top surfaceand inclined lateral sides, and an angle θ between one of the lateralsides and a straight line perpendicular to the flat top surface may beabout 50° to about 70°. The inclined lateral side of the raised portionRP may be formed through an etch process. For example, the inclinedraised portion RP may be formed through a wet etch process. Theinclination angle θ of the raised portion RP may be adjusted in the wetetch process, by altering the etching time.

Then, after depositing a transparent conductive material on theprotective layer 130, the resultant structure is patterned through aphotolithography process, thereby forming the pixel electrode PE, whichis electrically connected with the drain line DL through the contacthole.

Next, the first alignment layer 140 is formed on the first insulatingsubstrate 110. Then, the first alignment layer 140 is rubbed by using arubbing roll. In this case, the first alignment layer 140 may be rubbedby rotating a rubbing roll around which the rubbing cloth is wound at arate of about 1500 rpm (rotations per minute) to about 2000 rpm. Whenthe rubbing roll rubs the first alignment layer 140, the rubbing rollpresses the first alignment layer 140. Thus, a portion of the firstalignment layer where the rubbing roll is touched becomes to be sunkenpartially with a certain depth, i.e. a rubbing depth. The rubbing depthmade by the rubbing roll from a surface of the first alignment layer maybe about 0.20 mm to about 0.30 mm. If necessary, various rubbing clothsmay be employed. The rubbing cloth includes a ground cloth formed bywarps and wefts or a cotton cloth having a filing yarn woven in the warpdirection of the ground cloth. The filing yarn may be woven in a V shapewhile protruding toward a rubbing surface.

The second substrate 200 includes the second insulating substrate 210provided thereon with the black matrix BM including an opaque material,and a color filter 220 is formed on the second insulating substrate 210having the black matrix BM through a photolithography process. Thecommon electrode 230 is formed on the color filter 220 by using atransparent conductive material, and the second alignment layer 240 isformed on the common electrode 230. Thereafter, the second alignmentlayer 240 is rubbed by using the rubbing roll in a process as describedabove for alignment layer 140, thereby manufacturing the secondsubstrate 200.

The liquid crystal composition is interposed between the first andsecond substrates 100 and 200 to form the liquid crystal layer 300.

As described herein, the liquid crystal display of the embodimentsincludes a liquid crystal composition having a high Tni that is usedwith a substrate that has a raised portion of predetermined thicknessand shape, so that the liquid crystal display of the embodiments has areduced defect rate. The following Table 1 lists the results of a defectevaluation performed on a number of liquid crystal displays. Each of theliquid crystal displays used for the evaluation was formed with asubstrate including a raised portion as described in the firstembodiment, and employs a liquid crystal composition according to either(i) the conventional, related art or (ii) the embodiments of the presentinvention. The first two columns of Table 1 list the composition,properties and defect rates for a first and second comparative examplehaving conventional liquid crystal compositions with Tnis of 75° C. orless. The remaining columns list the composition, properties and defectrates for six liquid crystal compositions according to the presentembodiments.

In Table 1, the rows labeled “defect evaluation” show the number ofliquid crystal displays having defects after the liquid crystal displayshave been stored at a temperature of 80° C. for 48 hours and then slowlycooled down in the oven for 12 hours from 80° C. to a room temperature.The liquid crystal displays used in the defect evaluation have about5000 pixel areas PA. If defects occur in 1000 or more from among about5000 pixel areas PA, the liquid crystal display is regarded asdefective. The rows labeled “defect evaluation” show the number ofliquid crystal displays having defects from among total liquid crystaldisplays that were tested. For example, an entry of “10/10” indicatesthat defects occur in all of ten liquid crystal displays having theliquid crystal composition listed in the column tested, and “ 3/10”represents that defects occur in three from among the ten liquid crystaldisplays tested. Defect evaluations were performed five times for eachliquid crystal composition on the number of liquid crystal displaysindicated by the entry.

For reference, the column labeled “V10” of “V-T curve” indicates thedriving voltage applied to the liquid crystal display to a point inwhich transmittance becomes 10%, “V50” represents a driving voltageapplied to the liquid crystal display to a point in which transmittancebecomes 50%, and “V90” represents a driving voltage applied to theliquid crystal display to a point in which transmittance becomes 90%.

TABLE 1 Comparative Comparative Example 1 Example 2 Liquid Liquid LiquidLiquid Liquid Liquid of liquid of liquid crystal crystal crystal crystalcrystal crystal crystal crystal composition composition compositioncomposition composition composition composition composition 1 2 3 4 5 6Liquid Neutral 35 41 32 31 39.5 40 45 48 crystal liquid (weight %)crystal 1^(st) polar 15 16 18 18 10 10 8.5 10 liquid crystal 2^(nd)polar 50 43 50 51 50.5 50 46.5 42 liquid crystal Physical Tni 74.4 74.680.2 80.1 79.5 80.5 80 79.5 Property Refractive 0.102 0.1031 0.113 0.1140.1154 0.1134 0.113 0.1126 index (Δn) Dielectric 11.4 12.7 13.0 12.713.8 14.0 14.1 14.0 anisotropy (Δ∈) Rotational 78.9 82 100.9 100.9 97 9992 91 viscosity (mPa · s) V-T V10 1.12 1.08 1.12 1.23 0.95 0.99 0.980.99 Curve V50 1.45 1.76 1.47 1.60 1.67 1.67 1.64 1.68 (V) V90 1.91 2.251.91 2.16 2.04 2.13 2.05 2.09 Evaluation Response 15.6 15.6 15.7 15.014.0 14.9 13.4 — speed (ms) Contrast 620 620 699 685 820 711 689 — ratioDefect once 3/3 3/3 0/3  0/3  1/3  0/10 0/10 0/10 Evaluation Twice 10/10— 0/6  0/6  1/3  — — — 3 times 10/10 — — 0/10 — 0/10 — — 4 times 10/10 —1/10 3/10 0/10 0/10 — — 5 times 10/10 — 0/10 — 0/10 — — —

As shown in Table 1, liquid crystal compositions 1 to 6 having acomposition ratio according to the embodiment of the present inventionhave Tnis of 79° C. or more. Although the liquid crystal compositions 1to 6, which have the composition ratio according to the embodiment, havegreater dielectric anisotropy and a higher response speed as comparedwith those of a conventional liquid crystal, liquid crystal compositions1 to 6 have defect rates that are much less than liquid crystalcompositions of the first and second comparative examples. AlthoughTable 1 shows whether the liquid crystal display has a defect or not, inthe case of liquid crystal display which did not have defects, thenumber of defects is less than 10 per 5000 pixel areas PA, that is, suchliquid crystal displays have good quality.

Although not shown in Table 1, additional defect tests were performed onliquid crystal displays according to the embodiments The tests wereperformed under the conditions as described for Table 1 except that thethickness of the data line DL and the angle θ between the lateral sideof the protective layer 130 and a straight line perpendicular to theflat top surface of the raised portion RP of the protective layer 130are varied. The test results are described below as follows.

When a liquid crystal composition having Tni of 80° C. is used withliquid crystal displays in which with the data lines DL have a thicknessof 2000 Å and 1500 Å, defects occurred in all of three liquid crystaldisplays tested in the case of the data line DL thickness of 2000 Å, andno defects occurred in the three liquid crystal displays tested in thecase of the data line DL thickness of 1500 Å.

When a liquid crystal composition having Tni of 80° C. is used withliquid crystal displays in which the inclination angle θ of theprotective layer 130 is 54° or 65° and the data line DL is formed at thethickness of 1500 Å, defects occurred in all three liquid crystaldisplays tested in the case of the 54° inclination angle θ, and nodefects occurred in the three liquid crystal displays tested in the caseof the 65° inclination angle θ. Although defects occur in 1000 or morefrom among about 5000 pixels in the case of the 54° inclination angle θ,defects occur in 10 or less from among about 5000 pixels in the case ofthe 65° inclination angle θ.

As described above, according to the liquid crystal display of theembodiment of the present invention, defects are reduced, so thatdisplay quality can be improved. The liquid crystal display can be maderelatively easily through the manufacturing method described herein.

According to the embodiment of the present invention, when the liquidcrystal composition is used for the liquid crystal display, the weaknessof the liquid crystal composition for a high temperature is improved andthe raised portion RP of the protective layer 130 is minimized, therebyreducing defects in each pixel area PA.

Although the exemplary embodiments=have been described, it is understoodthat the present invention should not be limited to these exemplaryembodiments but various changes and modifications can be made by oneordinary skilled in the art within the spirit and scope of the presentinvention as hereinafter claimed.

1. A liquid crystal display comprising: a first substrate comprising afirst insulating substrate including a pixel area, a gate line formed onthe first insulating substrate, a data line crossing the gate line, anda thin film transistor connected to the gate line and the data line; asecond substrate opposite to the first substrate; and a liquid crystalcomposition interposed between the first and second substrates, whereinthe liquid crystal composition has a nematic-isotropic phase transitiontemperature (Tni) of 79° C. or above, and comprises: 31 weight % to 48weight % of a neutral liquid crystal comprising at least one compoundselected from the group consisting of formula 1, 8.5 weight % to 18weight % of a first polar liquid crystal comprising at least onecompound selected from the group consisting of formula 2, and 42 weight% to 51 weight % of a second polar liquid crystal comprising at leastone compound selected from the group consisting of formula 3,

wherein X is an alkyl, alkoxy, or alkenyl group having 2 to 5 carbonatoms and Y is an alkyl or alkenyl group having 2 to 5 carbon atoms. 2.The liquid crystal display of claim 1, wherein the liquid crystalcomposition has positive dielectric anisotropy in a range of about 8 toabout
 15. 3. The liquid crystal display of claim 2, wherein the liquidcrystal composition comprises a cholesteric liquid crystal compositionincluding a chiral liquid crystal having a pitch of about 50 μm to about70 μm.
 4. The liquid crystal display of claim 2, wherein a drivingvoltage applied to the liquid crystal layer is in a range of about 3.0 Vto about 3.6 V.
 5. The liquid crystal display of claim 1, wherein thedata line has a thickness of about 1500 Å or less.
 6. The liquid crystaldisplay of claim 5, wherein the data line comprises aluminum (Al). 7.The liquid crystal display of claim 5, further comprising a protectivelayer disposed on the first insulating substrate, wherein the protectivelayer has a raised portion with a height over the data line of about1400 Å or less.
 8. The liquid crystal display of claim 7, wherein theraised portion has a flat top surface and inclined lateral sides, and anangle between at least one of the lateral sides and a straight lineperpendicular to the flat top surface is in a range of about 50° toabout 70°.
 9. The liquid crystal display of claim 8, further comprisinga pixel electrode disposed in the pixel area and connected with a drainelectrode of the thin film transistor; a storage line spaced apart fromthe gate line on the first insulating substrate; and a storage electrodebranching from the storage line to partially overlap with the pixelelectrode and the data line.
 10. The liquid crystal display of claim 9,further comprising a gate insulating layer interposed between the dataline and the storage electrode.
 11. The liquid crystal display of claim8, further comprising a pixel electrode disposed in the pixel area andconnected with a drain electrode of the thin film transistor; and firstand second floating storage electrodes spaced apart from the gate lineon the first insulating substrate, partially overlapping with the pixelelectrode, and spaced apart from each other with the data line betweenthe first and second floating storage electrodes when viewed in a planview.
 12. The liquid crystal display of claim 11, further comprising agate insulating layer disposed on the gate line, wherein the first andsecond floating storage electrodes are disposed on the gate insulatinglayer.
 13. A method of manufacturing a liquid crystal display, themethod comprising: forming a gate line, a data line crossing the gateline to define a pixel area, and a thin film transistor connected to thegate line and the data line on a first insulating substrate; forming afirst alignment layer on the first insulating substrate and rubbing thefirst alignment layer to form a first substrate; forming a secondalignment layer on a second insulating substrate and rubbing the secondalignment layer to form a second substrate; and placing a liquid crystalcomposition between the first and second substrates, wherein the liquidcrystal composition has a nematic-isotropic phase transition temperature(Tni) of 79° C. or above, and comprises: 31 weight % to 48 weight % of aneutral liquid crystal comprising at least one compound selected fromthe group consisting of formula 1, 8.5 weight % to 18 weight % of afirst polar liquid crystal comprising at least one compound selectedfrom the group consisting of formula 2, and 42 weight % to 51 weight %of a second polar liquid crystal comprising at least one compoundselected from the group consisting of formula 3

wherein X is an alkyl, alkoxy, or alkenyl group having 2 to 5 carbonatoms and Y is an alkyl or alkenyl group having 2 to 5 carbon atoms. 14.The method of claim 13, wherein the data line has a height of about 1500Å or less.
 15. The method of claim 14, further comprising forming aprotective layer on the first insulting substrate which comprises araised portion with a height over the data line of 1400 Å or less 16.The method of claim 15, wherein the raised portion on the data line hasa flat top surface and inclined lateral sides, and an angle between atleast one of the lateral sides and a straight line perpendicular to theflat top surface is in a range of about 50° to about 70°.
 17. The methodof claim 13, wherein the first and second alignment layers are rubbedwith a rubbing roll rotated at a rate of about 1500 rpm to about 2000rpm, respectively, and a rubbing depth of the rubbing roll from asurface of the first and second alignment layers is in a range of about0.20 mm to about 0.30 mm.
 18. The method of claim 17, wherein therubbing roll is wound with a rubbing cloth and the rubbing clothcomprises a ground cloth formed by warps and wefts and a filing yarnwoven in a direction of the warp of the ground cloth.